Brake disc assembly

ABSTRACT

A floating brake disc assembly ( 10 ) has a hub member ( 14 ) and a rotor ( 12 ) mounted to the hub member for rotation therewith, the rotor being capable of moving in an axial direction of the disc relative to the hub member to a limited extent. A number of drive members ( 38 ) are rigidly attached to the rotor for engagement in corresponding cutouts ( 36 ) in the hub member, the drive members being movable in an axial direction of the disc relative to the cutouts as the rotor moves axially relative to the hub member. The axial movement of the rotor relative to the hub member is limited by corresponding stop means ( 26, 34   a   ; 46, 34 B) associated with the rotor and the hub member respectively. A friction means ( 60 ) is provided to resist, at least initially, axial movement of at least one of the drive members relative to its corresponding cutout. The friction means introduces a predetermined level of hysteresis into the floating disc mechanism to reduce rattle and vibration.

The present invention relates to a brake disc assembly. In particular,the present invention relates to a brake disc assembly of the floatingtype in which a brake rotor is mounted to a hub member in a manner whichallows the rotor to move axially relative to the hub member to a limitedamount, whilst being constrained to rotate with the hub member.

It is known to provide a brake disc assembly in which a brake rotor isrigidly mounted to a hub member. For use with standard productionvehicles, the brake rotor and hub are often produced as a one piececomponent. For higher performance vehicles, it is known to produce abrake disc assembly having a brake rotor that is rigidly attached to thehub, either by means of bolts or rivets.

It is also known to provide a brake disc assembly of the floating type,in which the rotor is mounted to the hub member so that it can moveaxially relative to the hub member to a limited extent. Floating discassemblies offer a number of advantages over brake disc assemblies inwhich the rotor is rigidly connected to the hub member. These include:

-   -   improved thermal stability as a result of removing the radial        constraint present in any rigidly mounted brake rotor, this        leads to a reduction in coning;    -   reduced tendency for build up of disc thickness variation (DTV)        as axial movement of rotor relative to hub effectively        eliminates run-out of the rotor relative to the hub;    -   reduced transmission of vibration created at the interface of        rotor and pad;    -   resistence to cracking which can be caused by stresses induced        in a rigidly mounted disc rotor by thermal variations.

These and other advantages of floating type brake disc assemblies arewell known in the art.

It is also known to provide floating brake disc assemblies in which therotor is connected to the hub member by means of a number ofcircumferentially spaced, axially extending bobbins or drive members. Inone known arrangement, the rotor is rigidly attached to the bobbinswhich are received in cutouts or recesses in the hub member. The bobbinsare capable of limited axial movement relative to the cutouts and haveradially extending, circumferential end faces that engage with opposingradial faces of the cutouts to transmit torque between the rotor and thehub member.

The above known arrangement has been used extensively for highperformance racing vehicles. However, the arrangement has not been foundto be suitable for vehicles intended for general road use. This isbecause movement of the rotor relative to the hub can lead to rattleand/or vibration caused by contact between the stops used to limit theaxial movement of the rotor relative to the hub. Whilst such rattle andvibration can be tolerated in a racing vehicle, it is not acceptable ina general road going vehicle and is particularly unacceptable in respectof high value, high performance vehicles where correspondingly highlevels of refinement are expected.

In an attempt to reduce the rattle and vibration in a floating typebrake disc assembly to acceptable limits, it is known to use a springmeans to provide an axial pre-load between the rotor and the hub member.EP 1 094 229, for example, shows a brake disc assembly in which therotor is connected to a hub member by a plurality of rivets that engagein opposing semi-circular recesses in the rotor and the hub. A conicalspring is located between an end flange of each rivet and the rotor andhub. Whilst this arrangement helps to reduce rattle and vibration, it isnot ideal as it results in a reduction in the efficiency of the floatingrotor arrangement. This is because the axial pre-load, whilst relativelylight, nevertheless may prevent the rotor from adopting an optimal axialposition with regard to the hub member. As a result there is a risk ofinducing DTV as the axial position of the floating rotor will to someextent be influenced by the run-out of the assembly.

There is then a need for an improved floating type brake disc assemblyin which the above problems are obviated or at least substantiallyreduced.

In particular there is a need for a floating type brake disc assembly inwhich rattle and vibration are reduced without unduly reducing theefficiency of the floating rotor assembly.

In accordance with the invention, there is provided a brake discassembly comprising a hub member and a rotor mounted to the hub memberfor rotation therewith, the rotor being capable of moving in an axialdirection of the disc assembly relative to the hub member to a limitedextent, at least one drive member rigidly attached to one of the rotoror the hub member and being received in a corresponding cutout in theother of the rotor or the hub member, the drive member being movable inan axial direction of the disc assembly relative to the cutout as therotor moves axially relative to the hub member, the drive member havingradially extending faces for contact with opposing faces of thecorresponding cutout to transmit torque between the rotor and the hubmember, characterised in that said axial movement of the rotor relativeto the hub member is limited by corresponding stop means associated withthe rotor and the hub member respectively and in that a friction meansis provided to resist, at least initially, axial movement of the drivemember relative to its corresponding cutout.

The provision of a friction means operative between the drive member andits cutout introduces hysteresis into the mechanism. The level ofhysteresis is selected or pre-determined so that it reduces rattle andvibration to acceptable levels without significantly reducing theefficiency of the floating rotor arrangement. A particular advantage ofthe brake disc assembly in accordance with the invention is that noaxial pre-load is applied between the rotor and the hub member.

Preferably, the friction means is operative between at least one of theradially extending faces of the drive member and an opposing face of thecutout. More preferably, the friction means is operative between aradially extending face of the drive member and an opposing face of thecutout which are adapted, in use, to transmit breaking forces betweenthe rotor and the hub when the disc assembly is braked whilst rotatingin a forward direction. In one embodiment, the friction means isoperative between a normally leading face of the drive member and anopposing face of the cutout.

Preferably, the friction means comprises a resilient means which may bein the form of a spring clip.

Preferably, the resilient means is at least partially received in arecess formed in one of a radially extending face of the drive member oran opposing face of the cutout and is adapted to contact the other ofsaid radially extending face or said opposing face.

Preferably, the resilient means is at least partially received in arecess formed in a radially extending face of the drive member.

Preferably, the resilient means can be compressed into the recess toenable direct contact between said radially extending face and saidopposing face when braking forces are transferred from the rotor to thehub member through said faces.

Preferably, the recess is curved.

Advantageously, where the resilient means is a spring clip, the clip canbe generally D-shaped in cross section, the curved portion beingreceived in the recess. The spring clip may be split at the apex of theD.

Preferably, the resilient means applies a pre-load acting in thedirection of the applied braking force when the disc assembly is brakedwhilst rotating in a forward direction in use.

Preferably, there are a plurality of circumferentially spaced drivemembers, a friction means being provided in respect of at least one ofthe drive members. More preferably, the number of friction meansprovided on the disc assembly is selected such that the overall level ofhysteresis introduced into the floating rotor mechanism is adapted tosuit the particular application.

Preferably, the friction means is arranged to provided a pre-determinedlevel of friction between the drive member and the cutout.

An embodiment of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings in which:

FIG. 1 is a perspective, exploded view of part of a brake disc assemblyin accordance with the invention;

FIG. 2 is a cross sectional view through part of the brake disc assemblyof FIG. 1 in an assembled condition;

FIG. 3 is a cross sectional view through part of the brake disc assemblyof FIGS. 1 and 2 taken on line B-B of FIG. 2; and

FIG. 4 is a perspective view of a drive member or bobbin forming part ofthe brake disc assembly of FIGS. 1 to 3.

With reference to the drawings, a brake disc assembly 10 in accordancewith the invention comprises a rotor 12 and a hub member 14. The rotor12 and the hub member 14 can be made of any suitable material forexample cast iron, steel, aluminium, or carbon. If required, the rotor12 and hub member 14 can be made of different materials.

The rotor 12 has two generally annular discs of material 16, 18 joinedby a plurality of vanes 20 to provide an air gap between the discsthrough which cooling air can circulate. This arrangement is well knownin the art, being referred to as a ventilated rotor. Each of the discs16, 18 has an outer surface 22, 24 for contact with a brake pad in aknown manner. One of the discs 18 has a number of mounting lugs 26 thatproject radially inwardly from its inner circumference for mounting therotor to the hub member 14, as will be described in more detail below.

Whilst it is preferred that rotor 12 is a ventilated rotor, it should beunderstood that the invention can be applied equally to a disc assemblyhaving a solid or non-ventilated rotor.

The hub member 14 is of the type commonly referred to in the art as a“mounting bell” and has a generally axially extending body portion 28. Afirst radial flange 30 projects inwardly from one end of the axial bodyportion 28 and has a number of holes 32 by which the hub member can bemounted to a hub (not shown) of a vehicle in proximity with a wheel(also not shown). The hub member 14 has a second radial flange 34 thatprojects outwardly from the other end of the generally axially extendingbody portion 28. A number of circumferentially spaced cutouts 36 areprovided in second radial flange 34. The number and position of thecutouts corresponding to the number and position of the mounting lugs 26on the rotor 12.

The geometry of the mounting bell is unrelated to the function of theinvention. Thus depending on the application, the hub member maycomprise a mounting bell that is offset inboard or outboard or may evenbe flat.

The cutouts 36 are generally “U” shaped and are adapted to receive drivemembers or bobbins 38 for connecting the rotor 12 to the hub member 14.As can be seen best from FIG. 4, each bobbin 38 has a main body potion40 that is generally rectangular in cross section. The main body portion40 is received in a respective cutout 36 with a small clearance fit inthe circumferential direction. A hole 42 is provided through the centreof the bobbin though which a bolt 44 can pass for attaching the bobbinto a respective mounting lug 26 of the rotor 12. A part circular radialflange 46 is provided at one end of the main body portion 40 and issized so as to extend beyond the edges of a respective cutout 36.

Mounting of the rotor 14 to the hub member 12 can be best seen in FIG.2. A bobbin 38 is located in each of the cutouts 36 so that the partcircular flanges 46 overlie the second radial flange 34 of the hubmember on the side which is outermost in use. The rotor 12 is positionedso that the mounting lugs 26 are aligned with the opposites ends of thebobbins 38 from the part circular flanges 46 and bolts 44 are insertedthrough the holes 42 in the bobbins and through corresponding holes 48in the mounting lugs 28. Nuts 50 are fitted to the bolts 44 andtightened to rigidly attach the rotor 12 to the bobbins 38. Washers 51may be positioned between the nuts 50 and the mounting lugs 26 asrequired.

Whilst in the preferred embodiment the bobbins 38 are attached to theirrespective mounting lugs 28 by means of a nut and bolt, this is notessential and it will be appreciated that any suitable fastening methodcan be used. For example, the bobbins 38 can be attached to the mountinglugs 26 by means of rivets or any other suitable fastener.

The direction of rotation of the brake disc assembly 10 when it isfitted to a vehicle that is travelling forwardly is indicated in FIG. 1by the arrow C, this will be referred to as the “forward direction” ofrotation of the disc. The main body portion 40 of each bobbin 38 hasfirst and second radially extending circumferential end faces 52, 54. Ascan be seen, the first circumferential end face 52 of each bobbin willbe the trailing face when the disc is rotated in the forward directionof rotation. This face will be referred to as the normally trailing face52. The second end face 54 will be referred to as the normally leadingface 54.

In order to brake an associated vehicle to which the disc 10 is fitted,a braking force is applied to the rotor 12 by means of a brake caliper(not shown) which biases brake pads (also not shown) into contact withthe outer faces 22, 24 of the rotor 12 in a manner well known in theart. When the associated vehicle is travelling forwardly, the discassembly will be rotated in the forward direction of rotation C aspreviously described. If a braking force is applied to the rotor 12 withthe disc rotating in the forward direction, the normally trailing faces52 of the bobbins will contact the opposing radial faces 56 of theirrespective cutouts 36, to transmit braking forces from the rotor 12 tothe hub member 14.

When a vehicle to which the disc assembly 10 is fitted is travelling inthe reverse direction, the disc assembly will be rotated in thedirection opposite to arrow C, which will be referred to herein as the“reverse direction” of rotation of the disc assembly, in which case thenormally trailing face 52 of the bobbing will become the leading face.When a braking force is applied to the rotor 12 of a disc assemblyrotating in the reverse direction, the normally leading faces 54 of thebobbins will contact their opposing radial faces 58 of the cutouts totransmit braking forces from the rotor 12 to the hub member 14.

With the rotor 12 mounted to the hub member 14 as described above, axialmovement of the rotor relative to the hub member is limited by contactbetween the rotor mounting lugs 26 and the inner face 34A of the secondradial flange 34 of the hub member, and by contact between the partcircular bobbin flanges 46 and the outer face 34B of the second radialflange 34. Thus the mounting lugs 26 and inner face 34A of the secondradial flange act as corresponding stops associated with the rotor andhub member respectively to limit the axial movement of the rotorrelative to the hub member in a first axial direction, whilst the bobbinflanges 46 and the outer face 34B of the second radial flange act ascorresponding stops associated with the rotor and hub memberrespectively to limit axial movement of the rotor relative to the hub inthe opposite axial direction.

The axial length of the main body portion 40 of the bobbins is slightlylarger than the axial thickness of the second radial flange 34 so thatthere is a small axial clearance or float X between the part circularflanges 46 on the bobbins and the outer face 34B of the second radialflange. This clearance X enables the bobbins 38 to move in the directionof the axis of rotation of the brake disc assembly to a limited extentand so allows the rotor 12 to float axially relative to the hub member14.

To control the axial movement of the rotor 12 relative to the hub member14 and to reduce unwanted vibration and/or rattle, a friction means isprovided in association with each of the bobbins 38 and which actbetween the bobbins 38 and their respective cutouts 36. In the preferredembodiment the friction means is in the form of a spring clip 60 locatedin a part circular or curved recess 62 formed in the normally leadingface 54 of the main body portion 40 of each bobbin. The spring clips 60are generally “D” shaped in cross section with a split at the apex ofthe D as indicated at 64. As can be seen best from FIG. 4, when a springclip 60 is fitted into the recess 62 of a bobbin, the flat face portion66 of the clip projects slightly beyond the normally leading face 54.The arrangement is such that when a bobbin is inserted into itsrespective cutout, the flat face portion 66 the spring clip is biassedinto contact with the opposing face 58 of the cutout. Frictional contactbetween the spring clip 60 and the opposing face 58 resists, at leastinitially, axial movement of bobbin in the cutout and so introduceshysteresis into the system.

Although the disc assembly 10 of the present embodiment comprises aspring clip 60 or friction means in respect of each of the bobbins 38,this is not necessarily the case and a spring clip 60, or other frictionmeans, may be provided in respect of only some or even only one of thebobbins or drive members 38 as will be discussed in more detail later.

The level of the friction force generated by the spring clips 60 isselected or pre-determined within acceptable limits so that it issufficient to prevent or reduce unwanted movement of the rotor, whichmight result in rattling or vibration, but is not so high that itsignificantly reduces the efficiency of the floating mechanism,preventing the rotor 12 moving axially relative to the hub member 14 tocompensate for runout in the assembly. A particular advantage of thespring clips 60 of the present invention when compared to the prior artis that the pre-load of the clips acts circumferentially rather thanaxially and so does not unduly influence the axial alignment of therotor 12 relative to the hub 14.

As described earlier, during forward travel of an associated vehicle towhich the brake disc assembly 10 is fitted, braking forces aretransmitted from the rotor 12 to the hub member 14 through the normallytrailing faces 52 of the bobbins 38 and the opposing faces 56 of thecutouts. Since most braking will occur during forward travel, it ispreferred that the spring clips 60, or other friction means, arearranged to act between the normally leading faces 54 of the bobbins andthe opposing faces 58 of the cutouts 36 as described. This has theadvantage that the pre-load of the clips is in the direction of appliedbraking force when the disc is braked whilst moving in the forwarddirection of rotation. However, the clips 60, or other friction means,could, either alternatively or additionally, be provided to act betweenthe normally trailing faces 52 of the bobbins and the opposing faces 56of the cutouts if required.

Although braking occurs predominantly during forward travel of avehicle, some braking will occur when the vehicle is travelling inreverse. As described previously, when a vehicle to which the discassembly 10 is fitted is braked when travelling in reverse, the brakingforces are transferred from the rotor 12 to the hub 14 through thenormally leading faces 54 of the bobbins and the opposing faces 58 ofthe cutouts. A particular feature of the present embodiment is that thespring clips 60 can be compressed into the recesses 62 in the bobbinswhen the discs are braked in reverse travel, so that the normallyleading faces 54 of the bobbins 38 can come in to direct contact withthe opposing faces 58 of the cutouts enabling the braking forces to betransmitted directly between the contacting faces 54, 58 rather thanthrough the spring clips 60.

The spring clips 60 can be made of any suitable material able to retainits required properties at the maximum operating temperature of thebrake disc assembly. For example, the spring clips 60 may be made from anickle-chromium alloy which may be from the Nimonic range of alloys.

Whereas the spring clips 60 have been described as being mounted inrecesses 62 formed in the normally leading face of the bobbins 38, thisneed not be the case. The spring clips could, for example, be mounted inrecesses formed in the normally trailing faces 52 of the bobbins orcould be mounted in recesses formed in one or both of the opposing faces56, 58 of the cutouts and arranged to contact a corresponding one of theradially extending faces 52, 54 on the bobbins. Furthermore, it shouldbe understood that the spring clips need not be D-shaped in crosssection and that any suitable form of spring clip or other resilientmeans can be used. Indeed the friction means need not comprise aresilient means at all, for example, suitable friction materials couldbe applied to one or more of the radially extending faces 52, 54 of thebobbin and/or to one or more of the opposing faces 56, 58 of thecutouts.

In a brake disc assembly in accordance with the invention, the overalllevel of hysteresis or friction introduced into the floating rotormechanism can be tuned to suit the requirements of any particularapplication. Application factors that may influence the level ofhysteresis or friction required include the disc diameter and mass,deflection of the hub bearing under cornering loads, influence of thebrake caliper type and general levels of refinement of the host vehicle.

In the preferred embodiment, for example, the pre-load on each of thespring clips 60 and/or the number of clips 60 provided on the disc canbe varied in order to adjust the overall level of hysteresis or frictionas required. Hence it may be found that for some applicationssatisfactory performance can be achieved if a spring clip 60, or otherfriction means, is provided in respect of only some, or indeed only one,of the bobbins 38. In particular, it may be that a spring clip 60, orother friction means, need only be provided on every alternate bobbin.

Whereas the invention has been described in relation to what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not limited to thedisclosed arrangements but rather is intended to cover variousmodifications and equivalent constructions included within the scope ofthe invention as claimed. For example, the bobbins or drive members 38could be rigidly attached to the hub member 14 and arranged to engage incutouts in the rotor 12. Those skilled in art will also appreciate thatthe precise number of drive members or bobbins 38 used to connect therotor 12 and the hub member 14 is not essential to the invention and canbe varied according to requirements.

1. A brake disc assembly comprising a hub member and a rotor mounted tothe hub member for rotation therewith, the rotor being capable of movingin an axial direction of the disc assembly relative to the hub member toa limited extent, at least one drive member rigidly attached to one ofthe rotor or the hub member and being received in a corresponding cutoutin the other of the rotor or the hub member, the drive member beingmovable in an axial direction of the disc assembly relative to thecutout as the rotor moves axially relative to the hub member, the drivemember having radially extending faces for contact with opposing facesof the corresponding cutout to transmit torque between the rotor and thehub member, characterized in that said axial movement of the rotorrelative to the hub member is limited by corresponding stop meansassociated with the rotor and the hub member respectively and in that afriction means is provided to resist, at least initially, axial movementof the drive member relative to its corresponding cutout.
 2. A brakedisc assembly as claimed in claim 1, in which the friction means isoperative between one of the radially extending faces of the drivemember and an opposing face of the cutout.
 3. A brake disc assembly asclaimed in claim 2, in which the friction means is operative between aradially extending face of the drive member and an opposing face of thecutout which are adapted, in use, to transmit braking forces between therotor and the hub when the disc assembly is braked whilst rotating inits reverse direction.
 4. A brake disc assembly as claimed in claim 3,in which the friction means is operative between a normally leading faceof the drive member and an opposing face of the cutout.
 5. A brake discassembly as claimed in claim 1, in which the friction means comprises aresilient means.
 6. A brake disc assembly as claimed in claim 5, inwhich the resilient means is a spring clip.
 7. A brake disc assembly asclaimed in claim 6, in which the resilient means is at least partiallyreceived in a recess formed in one of the radially extending face of thedrive member or an opposing face of the cutout and is adapted to contactthe other of said radially extending face or said opposing face.
 8. Abrake disc assembly as claimed in claim 7, in which the resilient meansis at least partially received in a recess formed in a radiallyextending face of the drive member.
 9. A brake disc assembly as claimedin claim 7, in which the resilient means can be compressed into therecess to enable direct contact between said radially extending face andsaid opposing face when braking forces are transferred from the rotor tothe hub member through said faces.
 10. A brake disc assembly as claimedin claim 7, in which the recess is curved.
 11. A brake disc assembly asclaimed in claim 7, in which the spring clip is generally D-shaped incross section, the curved portion being received in the recess.
 12. Abrake disc assembly as claimed in claim 11, in which the spring clip issplit at the apex of the D.
 13. A brake disc assembly as claimed inclaim 5, in which the resilient means applies a pre-load acting in thedirection of the applied braking force when the disc assembly is brakedwhilst rotating in its forward direction.
 14. A brake disc assembly asclaimed in claim 1, in which there are a plurality of circumferentiallyspaced drive members, a friction means being provided in respect of atleast one of the drive members.
 15. A brake disc assembly as claimed inclaim 13, in which the number of friction means provided on the discassembly is selected such that the overall level of hysteresisintroduced into the floating rotor mechanism is adapted to suit theparticular application.
 16. A brake disc assembly as claimed in claim 1,in which the friction means is arranged to provide a pre-determinedlevel of friction between the drive member and the cutout. 17.(canceled)